1. Field of the Invention
This invention relates generally to high speed machining equipment, and more particularly to an improved rotary union for delivering a lubricant/coolant to a tool bit to thereby increase the production rate of metal parts being produced.
2. Discussion of the Prior Art
Rotary unions are commonly used on machine shop tools, such as milling machines, jig bores, engine lathes, drill presses, shapers, planers, etc., to deliver a cooling liquid directly to the location where the cutting tool or bit contacts the workpiece. Typically, a rotary spindle supports a cutting tool or bit in a chuck. Both the rotary spindle and the cutting tool or bit are tubular such that a cooling/lubricating liquid can be made to flow through the lumens thereof and exit the tool bit at its cutting surface. The rotary union is the mechanism that allows introduction of the cooling/lubricating liquid or compressed air into the lumen of the machine tool's spindle from a stationary source, such as a high-pressure pump.
When performing deep boring or drilling operations, it is advantageous to deliver the coolant liquid under high-pressure at the cutting surface of the bit to effectively blast away metal chips from the bore as it is being formed. By removing the metal chips while effectively cooling the bit, boring, milling, drilling other metal working operations can be completed in a considerably shorter time than when the coolant/lubricant is merely flooded on the surface of the workpiece. The rotary union, thus, provides a way to deliver the liquid coolant to a rotating tool in a machining operation.
A popular prior art rotary union for use with metal working machines is that sold by the Deublin Company of North Brook, Ill. The Deublin product is described in the Kubala Patent 4,976,282. A shortcoming in the design of the rotary union of the type described in the Kubala patent centers on the type of high-pressure seal utilized therein. It incorporates a rotating seal member carried by the rotor of the coolant union and a rotating, floating seal member carried by a fluid pressure actuated device that urges the two seal members together when the liquid coolant, under pressure, is applied to the inlet port of the union. This type of seal has proven to be short lived, requiring frequent repair and replacement. Failure of the high-pressure seal allows the liquid coolant to reach the bearings, journaling the rotating shaft, washing away the bearing lubricant, ultimately leading to bearing failure. Also, the Deublin device cannot be used with compressed air when the spindle of the machine tool is running.
U.S. Pat. No. 4,449,739 to Raether discloses a rotary coupling for conducting a high-pressure liquid to a rotatable utilization device. The device disclosed in this patent is primarily intended for use in high-pressure, but low-speed applications, such as in rock drilling. The sealing rings described in this patent utilize alternating plastic and carbon sealing rings. In essence, the sealing rings function in the same manner as common chevron seals where the fluid pressure forces the plastic seals against the rotating shaft. The carbon rings are essentially just spacers, aiding in support of the plastic seal rings to inhibit extrusion of the plastic sealing rings. While such an arrangement may be workable at low rotational speeds, for machine tool applications where shaft speeds may approach 20,000 rpm, the arrangement shown in the Raether et al. patent would not be suitable. The friction between the rotating shaft and the plastic seal rings would rapidly destroy the seal.
It is accordingly a principal object of the present invention to provide an improved rotary union for use with high rpm metal working machines of the type described having an improved bearing seal arrangement that significantly increases the mean time to repair such rotary coolant unions.
Another object of the invention is to provide a non-contact bearing seal arrangement for a rotary union of the type described that can operate at fluid inlet pressures of 2000 psi or more and whose shaft can be rotated in excess of 2500 rpm, e.g., up to 20,000 rpm, for prolonged periods of three years or more.